Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into individual device chips by applying a laser beam to the wafer in the condition where the focal point of the laser beam is set inside the wafer to thereby form a modified layer inside the wafer.
Description of the Related Art
A plurality of devices such as integrated circuits (ICs) and large scale integrations (LSIs) are formed on the front side of a wafer so as to be separated by a plurality of crossing division lines. The wafer thus having the plural devices is divided along the division lines into individual device chips by using a dicing apparatus or a laser processing apparatus, for example. The device chips divided from the wafer are used in electrical equipment such as mobile phones and personal computers.
Further, there has been proposed a technique including the steps of attaching a protective tape to the front side of a wafer, next grinding the back side of the wafer to thereby thin the wafer, and next applying a laser beam having a transmission wavelength to the wafer to the back side of the wafer along each division line in the condition where the focal point of the laser beam is set inside the wafer to thereby form a modified layer as a division start point inside the wafer along each division line (see Japanese Patent No. 3408805, for example).
According to the technique disclosed in Japanese Patent No. 3408805, the width of each division line can be reduced to thereby increase the number of device chips that can be manufactured from one wafer as compared with the case of using a conventional dicing apparatus to form a division start point along each division line.